You can try Gymboree in St John Building (near the peak tram station)
They have a 1 hour a day play gym where kids (6months old to 5 years old) gather to play and socialise. Call them up to ck for time schedule.

It is not really for special needs kids but my little girl (13 months old) learn to walk there..free entry if you are a member (life time membership fee for only HKD250 per family).